The present invention relates to a printer of the type that prints characters and the like by means of a printing head successively on a paper sheet fed on a platen roller, and more particularly to such a printer having the printing head devised so as to be changeable with another type printing head.
Conventional printers whose printing mechanism consists essentially of a platen roller and a printing head for printing characters on a paper sheet fed on the platen roller can be classified tentatively into three types by the type of printing head used: an ink-jet type, a thermal type and a printing ribbon type. Of these three types, the last printing ribbon type printer is outside the present invention.
The ink-jet type printer, in which the printing head is made up of a set of ink-jet nozzles combined with an ink fountain into a unit, has an advantage that the print face is clear and durable, and therefore, suitable for printing a formal document, definitive scientific data and others to be kept clear for a long term. However, the printer of this type has a disadvantage that the ink stored in the printing head may happen to be exhausted midway of printing continuously for a long time, for instance, in the case of printing a long series of data outputted from a scientific instrument automatically operating continuously. On the contrary, the thermal type printer, in which the printing head made up of a plurality of dot resistors thermally print characters on a thermal sensitive paper sheet, is free from such a disadvantage, but has a drawback that the printed characters are undurable and apt to fade away because the thermosensible paper is made to change color by heat and infrared radiations contained in the day light and ordinary lighting. Accordingly, the thermal type printer is unsuitable for printing a document or data to be kept clear for a long period of time.
Such being the case, in many science laboratories, these two types of printers have conventionally been used properly in accordance with different printing purposes.